This invention relates to a method for evaluating a surfactant. In another aspect, it relates to obtaining a quantitative measure of foam quality of form-producing surfactants. In another aspect, it relates to a test method for selecting suitable surfactants for use in steam-surfactant floods wherein foam is formed in the presence of steam. In another aspect, it relates to a method of evaluating such surfactants in the presence of a gas. In still another aspect, the invention relates to a method of evaluating foam-producing surfactants by measuring the resistance of a flow of gas through a sand pack containing first water and then the surfactant solution. In another aspect, it relates to a method of evaluating foam-producing surfactants by measuring the pressure drop while passing a gas through the sand pack containing water and then again measuring while passing a gas through the sand pack containing the surfactant solution. In yet another aspect, this invention relates to a method of evaluating foam-producing surfactants by measuring the pressure drop across the sand pack during continuous flow of both gas and water and then during continuous flow of both gas and surfactant solution. In still another aspect, it relates to testing the thermal stability of a surfactant by applying the test method both before and after a surfactant solution has been thermally aged.
Field tests have shown that significant amounts of incremental oil can be produced profitably using the steam-foam diversion process. In the steam-foam diversion process, the foaming surfactant is injected simultaneously with steam. A foam is produced with the steam in situ; and, consequently, the process is normally referred to as the steam-foam process. While the steam-foam diversion process has experienced good success in the field, only limited laboratory screening has been applied to select the best surfactant for the process.
The thermal stability of the surfactant is an important factor in selecting a surfactant for field applications. Many surfactants lose their ability to produce effective foams after a few hours at temperatures of about 325.degree. F. Nonionic surfactants have better thermal stability than anionic and possibly cationic surfactants, and, for that viewpoint, are preferred for field applications. However, if a screening test was available, one could accurately pick the best surfactant without using a speculative rule considering only one aspect of the many aspects that should be considered in choosing a surfactant.
Laboratory screening tests, therefore, would allow one to choose the best thermally stable surfactant with good foaming ability in order to provide the optimum diversion of steam from the "steamed-out" zones to less permeable zones which have not been exposed to much steam. The heating of these zones would result in improved oil recovery in cyclic-steam operations in heavy oil reservoirs. The choosing of a surfactant, therefore, is important to the efficiency and proficiency of the recovery process, and an accurate screening test used in choosing the best surfactant would be a very helpful and important tool in the overall recovery process.
U.S. Pat. No. 3,785,437 describes a method for determining the ability of polymers to shut off water in sand cores by determining the residual resistance factor (RRF). The residual resistance factor is defined as the initial permeability to brine divided by the final permeability to brine in the presence of gelled and entrapped polymer, and in the presence of residual oil saturation. The residual resistance factor to oil is defined as the initial oil mobility in the presence of connate water divided by the final oil mobility following the polymer treatment. The patentees, therefore, evaluate polymers in water floods. The tests are for the use of different liquid phases, e.g., thickened water and a driving fluid. However, the steam-foam diversion process utilizes steam, primarily a gaseous vapor, not a liquid. A screening method, therefore, making measurements on surfactants in the presence of a gas, e.g., nitrogen, would be more appropriate and more accurate in selecting the best surfactant for a steam-diversion process.
An object of the instant invention, therefore, is to provide for an accurate method of evaluating surfactants for a steam-diversion oil recovery process.
Another object is to allow one to change the concentration of a surfactant solution while testing the surfactant solution.
Another object is to provide such a method which simulates the presence of steam in an oil well.
Another object of the present invention is to provide for a more efficient and proficient steam-diversion oil recovery process through the selection of a proper surfactant.
Yet another object is to provide a method of determining the thermal stability as well as the foaming ability of a surfactant.
These and other objects, aspects, and the several advantages of this invention will be apparent to those skilled in the art upon a study of this disclosure, the drawings, and the appended claims.